The invention relates to a method of creating a wellbore in an underground formation comprising drilling a borehole in the underground formation using a drilling tubular, capable of being expanded, to which a downhole motor driving a drill bit has been connected, and, after drilling to the desired casing setting depth, expanding the drilling tubular into place to line the borehole by applying a radial load to the drilling tubular and removing said load from the tubular after the expansion.
Expansion methods and devices are disclosed in German patent specification No. 1583992 and in U.S. Pat. Nos. 3,162,245 to Howard et al; 3,167,122 to Lang; 3,203,483 to Vincent; 3,326,293 to Skipper; 3,489,220 to Kinley; 3,785,193 to Kinley et al; 5,014,779 Meling et al; 5,031,699 to Artynov et al; 5,083,608 to Abdrakhmanov et al; and 5,366,012 to Lohbeck.
Many of the known expansion methods employ an initially corrugated tube and the latter prior art reference employs a slotted tube which is expanded downhole by an expansion mandrel.
The use of corrugated or slotted pipes in the known methods serves to reduce the expansion forces that need to be exerted to the tube to create the desired expansion.
It is an object of the present invention to provide a method for expanding a solid, i.e. unslotted, tubing which requires exertion of a force to expand the tubing and which provides a tubing having a larger diameter and higher strength than the unexpanded tubing and which can be carried out with a tubing which already may have a tubular shape before expansion.
There is provided a method of creating a wellbore in an underground formation comprising drilling a borehole in the underground formation using a drilling tubular, capable of being expanded, to which a downhole motor driving a drill bit has been connected, and, after drilling to the desired casing setting depth, expanding the drilling tubular into place to line the borehole by applying a radial load to the drilling tubular and removing the load from the drilling tubular.